Automatic expansion valve



Oct. 28, 1941. H. H. ROBSON AUTOMATIC EXPANSION VALVE 1939 2Sheets-Sheet 1 Filed Nov. 24

M a u i 5 Tm k WA Q ATTORNEY 1941a H. H. ROBSON AUTOMATIC EXPANSIONVALVE Filed Nov. 24, 1939 2 Sheets-Sheet 2 NW un mm Q wfi ah h QM! WM Nw mm, mm I II II "I ll pr f IT IN n u w- .cm NV I +Ill| II WW I [I]! V II f I! I INVENTOR 519: mvk k M ATT Patented Oct. 28, 1941 2,260,682 7AUTOMATIC EXPANSION VALVE Hector Harris Robson, Scarsdale, N. Y.,assignor to United Fruit Company, Boston, Mass., a corporation of NewJersey I Application November 24, 1939, Serial No. 305,812 I Claims.

This invention relates to expansion valves for use in refrigeratingsystems and its object is to provide an improved automatic control forthe valve which insures admission to the evaporator of precisely theright amount of refrigerant for optimum refrigeration under varyingconditions of temperature and pressure within the evapora-- tor. Thus,it is well known that in most systems maximum efiiciency is attained bymaintaining a slight amount of superheat at or adjacent the evaporatoroutlet or the compressor inlet and by my invention I am able so toregulate automatically the size of the valve opening as to admit thatamount of refrigerant which will maintain such superheat to within afraction of a degree F., for any normal range of pressure andtemperature fluctuations within the evaporator or for any change in thecapacity of the system. My system furthermore achieves that precision ofregulation even with refrigerants such as carbon dioxide which havecomparatively low critical temperatures and therefore which may bepresented to the expansion valve in the form of a gas or a liquid or amixture of both depending upon varying working conditions within thecondenser.

In the drawings:

Fig. 1 is a diagrammatic view of apparatus embodying my invention;

Fig. 2 is a side elevation view, partly in section, and Fig. 3 is an endelevation view; of y a motorized valve which I preferably employ.

In Fig. 1 the numeral 2 represents a compressor of usual constructionfor withdrawing refrigerant from the evaporator coil 4, through suctionheader 6 and pipe 8 and for forcing compressed refrigerant through pipeID to a condenser coil l2, whose turns are suitably cooled by anexternal medium. From the condenser l2 the condensed refrigerant passesthrough pipe 14 to an expansion valve l6 Where the fluid is expanded asit passes through outlet I8 and thence to the evaporator coil 4. Exceptas hereinafter indicated, all of the above described apparatus is ofconventional construction and operation.

The expansion valve 16 is shown enlarged in Figs. 2 and 3. It includesan inlet port 20 and an outlet port 22 to which the pipes l4 and I8respectively are connected. Communication between the two ports isregulated by valve 24 having a stem 32 screw threaded at 26 to mate witha corresponding screw thread 28 in the frame 30, so that rotation of thevalve stem 32 in one or the other direction moves valve 24 toward oraway from its seat 36. I have shown the seat sharp edged asis preferredfor precision in regulation of the amount of refrigerant passed from thecondenser into the evaporator. To open and close the valve, its stemcarries fixedto it a pinion 38 meshing with gear 40 which, in turn,meshes with pinion 42 on a countershaft 44 of motor 46. Speed reductiongears, not shown, within the motor casing connect the armature shaft ofthe motor with the shaft 44 so that when the motor is connected to asuitable source of power, shaft 44 rotates very slowly, such as at tworevolutions per hour. With shaft 44 rotating that slowly there need beno substantial reduction in gears 42, 40 and 38. The pitch of threads 26and 28 is low and as a, resultof the slow rotation of the stem, thevalve moves very slowly toward its open or closed positionswhen motor 46is operated. j

The motor 46 is reversible and in the embodiment shown I employ a directcurrent circuit leading to the three binding posts 50, 52 and 54. Withone direct current lead closed to the post 52, the motor will rotate ina direction to close the valve if the other direct current lead isclosed to post 56 and will be rotated in a direction to open the valveif that other lead is closed to p st 54.

The direct current power source is indicated by leads 60 and 62 (Fig.1). When switch 64 is closed lead 60 is connected through variableresistance 66 (adapted to regulate the speed of the motor in an obviousmanner) to the central binding post 52. Lead 62 is connected throughline 68 to contact lever 10 adapted to close circuit selectively tolines I2, 14 and I6. The switches and 82 are limit switches to bedescribed that are normally closed and, accordingly, when switch 10completes circuit to line 12 the valve will open very slowly. Whenswitch 10 is closed to line 16 the valve will rotate very slowly towardits closed position. When switch 10 contacts neither line 12 nor 16, butcloses circuit to line 14, the opening and closing of the valve isautomatically effected in the following manner, re-- sponsive tofluctuations in relative conditions of pressure and temperature withinthe suction header 6. Y

indicates a small tube communicating at one end with the suction header6 and its other end with a pressure responsive instrument 92 having anelement 94 which moves to the right,

as viewed in Fig. 1 when the pressure in the header 6 increases and tothe left when it decreases. Within the suction header 6 is a temperatureresponsive instrument such as a there mometer 96, connected by tube 98with a temperature responsive instrument I having an element I04 pivotedat I03 and moved to the right when the temperature in the header 6 risesand to the left when it falls. Also mounted on pivot I03 of thetemperature responsive instrument I00 is a lever I02 connected by link Ito element 94. Lever I02 is freely mounted on the pivot I03 and by thelink connection I05 is moved to the right or left upon a correspondingmovement of the pressure indicating element 94 when the pressure in theheader increases or decreases respectively,

Element I04 carries contact I06 adapted to close an electric circuitwith contact I08 carried by the lever I 02 when the relative positionsof elements 94 and I 04 are such that the contacts abut each other.Element I04 also carries contact IIO adapted to close circuit withcontact II2 fixed to lever I02 when the relative positions 'of theelements make those contacts abut each other. Element I04 is connectedto the line I4.

Element I04 and lever I02 are electrically insulated from each other.The line I6 is connected to terminal I08 and line I2 is connected toterminal II 2.

With the device constructed as above described, it will be apparent thatif switch I0 isclosed to line I4, thereby energizing temperatureindicating element I04, a relative movement either of pressureindicating element 94 or temperature indicating element I 04 such thatcontact is made from IIO to contact I I2, circuit will be completedthrough line I2 to terminal 54 of motor 46, thus rotating the valve stemin a direction to open the valve. On the other hand, if the relativepositions of pressure indicating element 94 and temperature indicatingelement I04 are such that contact is made from I06 to I08, circuit willbe completed to terminal 50 of motor 46 moving the valve toward closedposition. The limit switches 80 and 82 are provided to insureautomatically against such continued actuation of motor 46 as wouldforce the valve 24 beyond its extreme open or closed positions. As willbe seen from Fig. 2, the pinion 38 not only rotates in either directionbut moves to the right or to the left as the valve is opened or closedand the gear 40 is elongated to accommodate such movement. The pinion 38carries a pin having a portion Ia projecting rearwardly and a portionI20b projecting in front of the pinion. The gear rotates clockwise toclose the valve during which the pinion advances toward the frame memberI22. portion I20a as the valve nears its closed position is therotatably mounted lever I24, to which is secured switch arm 80 springpressed at I against the terminals 80a and 80b. Thus, the circuit isautomatically opened in the lead to binding post before the valve isinjured. Similarly, the pin portion I20b engages the lever I25 springpressed at I28 against terminals 82a and 82b to open circuit to thebinding post 54 as the valve-arrives at its extreme open position. Limitswitches of this character are well known and need not be furtherdescribed.

By suitably constructing lever I02 and spacing its contacts from thecorresponding contacts on temperature indicating element I04 I caneffect automatic movement of the valve toward its open or closedposition upon substantially any desired predetermined relativeconditions of temperature and pressure at whatever point the pressureand temperature are taken, in this in- Projecting into the path of pin 1stance at the outlet header 6. In practice, I have found that maximumefficiency of the system is attained by maintaining the refrigerantwhich reaches the suction header 6 at between 1 F. and 2 F. superheatsince thereby I insure maximum refrigerating effect within theevaporator, optimum conditions of heat interchange between evaporator 4and the medium to be cooled which surrounds it and maximum eificiency ofthe compressor. To obtain this 1 F. limit variation of control I sospace the contacts I08 and H2 from their corresponding contacts I06 andH0 that a relative movement equivalent to 1 F. between element I04 andlever I 02 commencing with either circuit being made will cause thatcircuit to be broken and the other to be made. I then adjust theposition of lever I02 with reference to temperature indicating elementI04 so that that 1 F. variation conforms to the range between 1 F. and 2F. superheat for Whatever pressure is registered by the element 64.Specifically, if carbon dioxide is employed as the refrigerant and atemperature of 33 F. is assumed to be the saturation temperature for apressure of 500 lbs. per square inch, I so position the parts in anobvious manner that relative to a pressure reading of that value onmeter 92 contact is made across terminals I06 and I08 to operate thevalve toward its closed position when a temperature of 34 F. is reached,and contact is made between points H0 and M2 to operate the valve towardits open position when a temperature of 35 F. is reached. Obviously,this same relationship will be maintained for the correspondingsuperheat temperatures when the pressure varies from 500 lbs. per squareinch.

It will be observed that after a change has been made in the position ofvalve I6, the effect of that change on the refrigerant in the coil isnot felt by the temperature and pressure responsive apparatus until therefrigerant reaches the suction header 6. It is partly to guard againstthe possibility of over regulation under those conditions that I providefor extremely slow movement of the valve by the motor 46 and in practiceI have found that over regulation is entirely obviated thereby. i

It will thus be apparent that the apparatus above described soautomatically effects opening and closing of the valve I6 that the sizeof valve opening is varied to meet precisely the loaddemand on theevaporatorfor all changes in pressure and temperature within it. Mysystem insures maintenance of that size valve opening which will producea predeterminedsuperheat under any changes in capacity of the system,whether resulting from differences in refrigerating load imposed by themedium to be cooled which surrounds the evaporator or from changes inthe speed of the compressor. Unlike prior automatic expansion valveswhich are operated. by the pressure difference between a thermostaticpressure on one side of a movable diaphragm and an actual pressure onthe other side, my apparatus insures the necessary variations in size ofthe valve opening for the same amount of superheat at differentpressures'and temperatures Within the evaporator and thus isparticularly effective to maintain maximum efficiency when the capacityof the system is in any way varied. Further-more, my system effects thissensitivity of controleven with gases, which like carbon dioxide havelow criticaltemperatures' and thereby may in commercial operation bepresented to the expansion valve either as a liquid or as, a gas, or

-ing from the principle of my invention. Thus,

although my invention .fills a need which has not heretofore beensupplied for automatic expansion valve regulation for use with carbondioxide refrigerant, its use is, of course, not limited thereto. Nor arethe specific temperatures above recited in any way essential as othersmay be required under different conditions of operation. Although thetemperature and pressure connections are preferably located within thesuction header, this is not essential as they can be located elsewhere.I prefer,'however,to dispose both connections in the same .part of thesystem. 'The direct current motor described as my preferred source ofpower for moving the valve may, of course, be replaced by any motivatorwhether electric, pneumatic, hydraulic or mechanical, as is desired. Itis contemplated that the contacts I08 and H2 be adjustably mounted onthe lever I02 so that the spacing between them, representing thelatitude of relative positions of lever I02 and member I04 throughoutwhich neither circuit is closed to the valve'motor, may-be varied atwill and that the length of connecting link I05 may be made adjustable.All such adjustable constructions are within the scope of my invention,although it is obviously unnecessary to illustrate them in detail in thedrawings.

I claim:

1. A refrigerating system adapted to operate at a substantially constantsuperheat throughout a range of temperatures in the system, comprising acompressor, condenser and evaporator connected in circuit, an expansionvalve admitting refrigerant to the evaporator, and means for operatingthe valve to maintain said superheat, said means comprising an elementmoved by changes in pressure in the system, a second element moved bychanges in temperature in the system and independently of the movementof the first element, and means responsive to a predetermined relativepositioning of said elements to move the valve toward its open positionand responsive to a second predetermined relative positioning of saidelements to move the valve toward its closed position.

2. A refrigerating system adapted to operate at a substantially constantsuperheat throughout a range of temperatures in the system, comprising acompressor, condenser and evaporator connected in circuit, an expansionvalve admitting refrigerant to the evaporator, and means for operatingthe valve to maintain said superheat, said means comprising an elementmoved by changes in pressure in the system, a second element moved bychanges in temperature in the system and independently of the movementof the first element, means responsive to a predetermined relativepositioning of said elements to move the valve toward its open positionand means responsive to a second predetermined relative positioning ofsaid elements to move the valve toward its closed position, the saidelements having a third predetermined relative positioning intermediatesaid first and. second relative positionings, corresponding to thedesired superheat, at which the valve remains stationary.

3. A refrigerating .system comprising a compressor, condenser andevaporator connected in circuit, an expansion valve admittingrefrigerant to the evaporator, and means for operating the valve tomaintain in the system a predetermined range of superheat, said meanscomprising an element .moved by changes in pressure in the system, asecond element moved by changes in temperature in the system and.independently of the movement of the first element, means responsive toa predetermined relative positioning of said elements to move the valvetoward its open position and means responsive to a second predeterminedrelative positioning of said elements to move the valve toward itsclosed position, the said elements having a predetermined rangeof'relative positionings intermediate said first and second relativepositionings, corresponding to a range of superheat, at which the sizeof the aperture remains unchanged, and means for changing saidrange ofrelative positionings to vary the range of superheat.

4. A refrigerating system adapted to operate at a substantially constantsuperheat throughout a range of temperatures in the system, comprising acompressor, condenser and evaporator connected in circuit, an expansionvalve admitting refrigerant to the evaporator, and means for operatingthe valve to maintain said superheat, said means comprising an elementmoved by changes in pressure in thesystem, a second element moved bychanges in temperature in the system and independently of the movementof the first element, one of said elements having two members movablewith the rest of the element as a unit and disposed in spaced relationrelative to each other, the other of said elements constituting a singlemember movable through the space separating said spaced members andadapted to engage said members at opposite limits of its said movement,means for moving the valve toward its open position when said singlemember engages one of said spaced members and means for moving the valvetoward its closed position when said single member engages the other ofsaid spaced members, said valve remaining stationary when said singlemember is not in engagement with either of said spaced members.

5. A refrigerating system adapted to operate at a substantially constantsuperheat throughout a range of temperatures in the system, comprising acompressor, condenser and evaporator connected in circuit, an expansionvalve having an aperture through which refrigerant is admitted to theevaporator, and means for operating the valve to maintain saidsuperheat, said means comprising an element moved by changes in pressureat a predetermined point in the system, a second element moved bychanges in temperature at substantially the same predetermined point inthe system and independently of the movement of the first element, poweroperated means for varying the size of said aperture by moving the valveselectively toward its open or closed positions, means responsive to onepredetermined relative positioning of said elements to actuate the poweroperated means for moving the valve toward its open position and meansresponsive to a second predetermined relative positioning of saidelements to actuate the power operated means for moving the valve towardits closed position, the said power operated means being adapted, whenactuated, to move the valve so slowly that the effect of a slight changein aperture size is felt at said predetermined point before anysubstantial change in aperture size is made.

6. A refrigerating system adapted to operate at a substantially constantsuperheat through-I out a range of temperatures in the system,comprising a compressor, condenser and evaporator connected in circuit,an expansion valve admitting refrigerant to the evaporator, and meansfor operating the valve to maintain said superheat, said meanscomprising an element moved through predetermined distance increments inresponse to predetermined changes in temperature at a given locationwithin the system, a second element moved through the same increments inresponse to the same predetermined changes in saturation temperaturecorresponding to changes in pressure at said location and independentlyof the movement of said first element, means responsive to apredetermined relative positioning of said elements to move the valvetoward closed position to prevent decrease below said superheat, andmeans responsive to a second predetermined relative positioning of saidelements to move the valve toward open position to prevent increaseabove said superheat.

7. In a superheat control for an expansion valve, the combination ofmeans for power operating said valve, independently movable pressure andtemperature responsive elements controlling said valve operating means,means for subjecting the said elements respectively to pressure andtemperature conditions prevailing at substantially the same point in asystem to cause said operating means to move the valve toward openposition at the upper limit of a predetermined range of superheat andtoward closed position at the lower limit of said range.

8. In a superheat control for an expansion valve, the combination of anelectric motor driving the valve and having one circuit for moving thevalve toward open position and a second circuit for moving the valvetoward closed position, a switch in said valve opening circuit, a switchin said valve closing circuit, independently movable pressure andtemperature responsive elements controlling said switches, means forsubjecting the said elements respectively to pressure and temperatureconditions prevailing at substantially the same point in a system toclose said switch in said valve opening circuit at the upper limit of apredetermined range of superheat and to close said switch in said valveclosing circuit at the lower limit of said range.

9. In a superheat control for an expansion valve, the combination of anelement adapted to be moved through predetermined space increments inaccordance with predetermined changes in temperature within a system, asecond element adapted to be moved through the same predetermined spaceincrements by the same predetermined changes in saturation temperaturecorresponding to changes in pressure within the system, means for movingthe valve toward open position when said elements are disposed in apredetermined relative position, and means for moving the valve towardclosed position when said elements are disposed in a secondpredetermined relative position.

10. In a superheat control for an expansion valve, the combination whichincludes a pair of members engageable to move the valve toward openposition at the upper limit of a superheat range, a pair of membersengageable to move the valve toward closed position at the lower limitof said range and apparatus for maintaining said range fixed fordifferent pressures and temperatures at a predetermined location withina system comprising means for moving one member of each pair throughpredetermined distance increments in response to predetermined changesin temperature at said location and means for moving the other member ofeach pair through the same increments in response to the same changes insaturation temperature corresponding to changes in pressure at saidlocation and independently of the movement of the first mentioned memberin each pair.

HECTOR HARRIS ROBSON.

